The present invention relates generally to a closed type battery, and more particularly to a closed type battery comprising a battery can and an electrode-drawing sheet that becomes an electrode terminal, to which a battery terminal of polarity opposite to that of the battery can is attached via an insulating member.
Various batteries are used as power sources for electronic equipments of miniature size, and miniature yet large-capacity closed batteries are employed as power sources for cellular phones, notebook PCs, camcorders, etc. Typically, closed batteries using a non-aqueous electrolyte such as lithium batteries and lithium ion rechargeable batteries are now used.
To keep pace with the downsizing of equipments, closed batteries of rectangular shape capable of making effective use of a small space, to say nothing of cylindrical batteries, are enjoying wide applications. In a typical rectangular battery, a battery can working as one electrode of the battery is provided with an electrode terminal while isolated therefrom by an insulating member.
One such typical example of the closed type battery of rectangular shape is shown in FIG. 2.
A closed type battery shown generally at 1 comprises a cylindrical form of rectangular metal package 2 (hereinafter often called the battery can) made of stainless steel, soft steel nickeled on its surface, etc., in which there is a battery element comprising a roll form of cathode and anode stacked one upon another via a separator. At the upper end of the battery can 2, there is a header 7 formed by integrating an external insulating sheet 4A and a cathode-side electrode drawing sheet 5 with a metal sheet 3 by means of a cathode-side electrode leading pin 6; this header 7 is mounted and sealed at the opening of the battery can 2. One portion of the header 7 is made thinner (shown at 8) than the rest thereof so as to let an abnormally rising internal pressure escape from the battery and another portion of the header 7 is provided with a hole 9 from which an electrolyte is poured in the battery assembly and which is sealed up after the pouring of the electrolyte. After the electrolyte is poured from the hole 9 into the battery assembly, a metal member such as a stainless steel member is embedded in the hole 9, and then welded thereto for sealing purposes.
One exemplary header is shown in FIGS. 3(A) and 3(B). FIG. 3(A) is illustrative in perspective of the header, and FIG. 3(B) is illustrative in section of the header in which a cathode-leading pin is ready for caulking.
An internal insulating sheet 4B formed of a polypropylene, fluorocarbon resin, etc. is mounted on a metal sheet 3 formed of a stainless steel sheet, a nickeled soft steel sheet, etc. by inserting a projection on the sheet 4B into a through-hole 10 formed in the sheet 3 from below. Then, an external insulating sheet 4A is placed over the upper surface of the sheet 3 to form an insulating member. Then, an electrode-leading pin 6 formed of a metal of good conductivity such as aluminum or an aluminum alloy and having a collar 6A is inserted through a hollow portion of the projection on the internal insulating sheet 4B, and an electrode-drawing sheet 5 is fitted in the external insulating sheet 4A. Finally, the collar 6A and the tip of a shaft 6B of the electrode-leading pin are caulked from above and below to form a header 7.
After joined to the collar 6A of the electrode-leading pin 6 of the thus prepared header 7, an electrically conductive tab 12 joined to the battery element and covered with an insulating member 11 is fitted into an opening of the battery can, and then laser welded at its periphery to seal up the opening.
Upon header assembling, the electrode-leading pin 6 is crushed by caulking into contact with the plane of the electrode-drawing sheet 5, so that a conductive connection is made between the electrode-leading pin and the cathode-drawing sheet 5. On the other hand, the lower surface of the electrode-drawing sheet 5 comes in contact with the surface of the external insulating sheet 4A for hermetic or airtight purposes.
Since the tab for the connection of the battery to an external circuit is soldered, welded or otherwise joined to the electrode-drawing sheet, however, it is likely that there will be a drop of hermeticity due to shrinkage by thermal hysteresis upon joining of the synthetic resin of the external insulating sheet or a sag of caulking.
A primary object of the present invention is to provide a closed type battery having an electrode-sealing structure sealed by caulking of an electrode-leading pin, which is improved in terms of insulation, hermecity and airtightness between an insulating sheet and an electrode-drawing sheet, and shows reduced changes with time and increased reliability.